Particularly for the demographic you’ve described, if there is any evidence for their occasion of sin being more or less grave than those who are not SSA, it is clearly that it is more an occasion of sin insofar as the number of sins committed by such persons is clearly higher on average than those who are not SSA.
Don’t oversimplify the phenomina of same-sex attraction (SSA). A greater number of sins being committed by people who experience SSA doesn’t necessarily mean that living together would be a greater occasion of sin.
Many NARTH psychologists hold that many times SSA is a symptom of a need for bonding with others of the same sex. Dr. Joseph Nicolosi writes:
“[Male] homosexual clients report that when they begin to know another man intimately, their sexual interest in him diminishes. It is always, they report, the distant person who is sexually attractive.”
-Joseph Nicolosi,
Reparatve Therapy of Male Homosexuality, page 120
This is important regarding this discussion for obvious reasons. What he says immediately afterwords reveals, in part, why many homosexual persons have short, promiscuous sexual relations:
“We see here the frustrating cycle of distant attraction and then close disinterest, a cycle of continual, and for so many, lifelong, frustrated desire for intimacy.”
This same psychologists and many other psychologists hold that individuals who experience SSA often tend to sin more often than others due to emotional problems that often drive their SSA.
Even supposing you’d like to debate that (I’d be happy to see any figures you’ve compiled), the principle still stands, and there isn’t a theological rationale for defending this opinion; I highly doubt there is even a modern-day moral theologian who would support it. The principle–especially with a former partner in sin–that one cannot live with in such circumstances is an absolute principle. Consider the moral theologians on the topic. No priest can validly administer the sacrament to such persons.
I think you have your mind set on the wrong principle. Avoiding the near occasion of sin is the moral principle behind this thread. The principle is very easy theoretically, that is, the principle that one must avoid situations that would make one more likely to sin. The application of this principle isn’t always so easy. Living with a person who one used to commit sexual sins with would, in most but not all situations, more likely lead one to sin, but not necessarily. If that is the case, than to live together would be a near occasion of sin, but if not, than living together would not be a near occasion of sin (and perhaps even the opposite).
This thread actually falls outside the realm of moral theology into the realm of social science since the application of the principle of moral theology in question in this situation (the near occasion of sin) depends on the effect the situation is likely to have on one’s behavior.
There is no universal, absolute, moral principle that one cannot live with a former sexual partner. Doing so would almost always be a near occasion of sin, but not necessarily.
Regarding figures, it’s extremely difficult to come up with numbers like these because its rare nowadays for young people to choose celibacy and probably rarer for an individual with SSA to convert to Catholicism.
The question is simple. Am I more or less likely to sin in this situation? The answer isn’t as obvious.
I’m not necessarily saying that the OP should or shouldn’t live with her former sexual partner. I am saying that if doing so would more likely lead to sin than she shouldn’t. On the other hand, if she would be less likely to sin living with her, than it would actually be good for her to do so. She should think long and hard about it, and petition God’s help as well.